This application claims a priority based on German Patent Application DE 199 01 391.8, filed Jan. 15, 1999, and the disclosure of that application is incorporated herein by reference.
The invention relates to a spotlight with an adjustable angle of radiation, wherein modification of the angle of radiation is achieved in a manner other than by shading a beam path with a screen or mask, having a light source arranged within the spotlight and a first lens that is a front lens of the spotlight. Profile projectors, in which small modifications of angles of radiation occur as a side effect during image focusing, do not belong to this class of spotlights.
Spotlights with adjustable angles of radiation as known in the prior art can be divided into three classes, namely stepped lens spotlights, spotlights with very deep reflectors, and spotlights with an optical unit, including a second lens, a light source, and a reflector, that is moveable relative to a front lens.
Conventional stepped lens spotlights have a single stepped lens (Fresnel lens). Incandescent bulbs, halogen bulbs, or discharge lamps are used as light sources in these stepped-lens spotlights. The light source and a reflector are mounted on a slide at a fixed distance from each other. The slide is movable relative to the Fresnel lens. Focusing is achieved by moving the slide. However, in stepped lens spotlights of this type, a significant effective loss of light occurs at focus settings with small angles of radiation. Since there is no second lens to concentrate the light toward the Fresnel lens, a large portion of the light emitted by the light source is simply absorbed by an inner wall of a housing at such focus settings, which results in loss of light and unneeded heating of the housing.
In general, a spotlight with a very deep reflector is constructed so that the lamp and reflector can be displaced relative to each other, but in these spotlights the lamp remains inside the reflector, along its optical axis, at all times. The angle of radiation of these spotlights is modified by changing the position of the lamp within the reflector. However, a focusing path that can be achieved in this way is minimal, so that an angle of radiation can be varied only within relatively narrow limits. Spotlights of this type do provide a high degree of light efficiency, but they exhibit unfavorable light distribution in nearly all lamp positions. A reason for this generally poor light distribution is that a particular fixed reflector shape provided respectively for each one of these spotlights, relative to a resulting light distribution, can be optimally designed for only a single lamp position. Uneven light distribution occurs when the lamp or the reflector are moved for focusing purposes, for example. Therefore, to improve light distribution, replaceable front lenses are often used in spotlights of this type. These lenses may have frosted properties, a honeycomb structure, or other specially formed features that serve to provide additional focusing or light dispersion, in which, however, aspherical front lenses have never before been used in spotlights with adjustable angles of radiation. With these spotlights, therefore, variously modified front lenses must be used for various angles of radiation. For many such spotlights with very deep reflectors, both the lamps and the reflectors are mounted in fixed positions in the housings, i.e. the angles of radiation are modified in such cases exclusively by replacing variously-shaped front lenses. This entails a relatively significant amounts of labor and time spent changing front lenses if such a spotlight is-used in a situation in which the angle of radiation must be often changed.
Spotlights with adjustable angles of radiation of the third group, in accordance with the above classification, are a significant improvement over the spotlights described above. Such a spotlight is disclosed by U.S. Pat. No. 4,823,243 and European Patent 0 846 913. This spotlight has a light source, a reflector associated with the light source, a first collector lens (front lens) placed in a beam path in a direction of a beam of the light source-reflector combination, and a second collector lens located between the light source and the first collector lens. The reflector, the light source, and the second collector lens are mounted as an optical unit that is movable relative to the first collector lens along an optical axis of the spotlight. Inside the optical unit disclosed in U.S. Pat. No. 4,823,243 a spacing between the light source and the second collector lens is adjustable. Very similar spotlights are also commercially available in which, however, mutual spacings between a reflector, a light source, and a second collector lens cannot be modified. In the latter spotlights, optical units can be moved only as fixed wholes. By contrast, in the spotlight disclosed in European Patent 0 846 913, within the optical unit that can be moved relative to the first collector lens, both the spacing between the light source and the second collector lens and the spacing between the light source and the reflector can be modified. Common to all the spotlights described in this paragraph, however, is that the front lens is a spherical lens.
The spotlights with adjustable angles of radiation specified in the previous paragraph, one of which is shown in a schematic view in FIG. 5, provide a large modification range of angles of radiation (see FIGS. 6a, 6b herein), and achieve a high degree of light efficiency in terms of energy required to operate spotlights. In addition, they provide exceptionally even light distribution. Moreover, such a spotlight no longer produces scattered light (light intensityxe2x89xa650% of maximum light intensity), as defined according to a conventional concept, owing to a sharp slope of the light intensity at the edge of the lighted area. As shown in FIGS. 6a, 6b, a characteristic illuminance curve of a lighted field does exhibit small increases in intensity at the edge, the size of which depends on the setting of the optical unit, but the light intensity across the entire lighted area is largely constant. Increases in intensity at the edge do not occur in the spot setting. They appear only upon movement of the spotlight out of the spot setting and then increase continuously in size until a critical setting in the angle of radiation between the spot setting and the flood setting is achieved, in which the size of the intensity increase at the edge reaches a maximum. Upon further movement of the spotlight in a direction toward the flood setting, the size of the intensity increase at the edge once again decreases continuously.
If graining, or pocking, is provided on a surface of the second lens so that a micro-lens structure arises on the grained surface, the intensity increase that occurs at the edge in the characteristic illuminance curve is dampened, but not entirely eliminated. Moreover, this reduction in intensity increase at the edge is achieved at a cost of increased scattering and loss of light.
It is an object of this invention to provide a spotlight of the type mentioned in the opening paragraph above that provides a more even light distribution, particularly in angle of radiation settings outside the spot setting, than do such spotlights known in the prior art.
According to principles of this invention, a spotlight, whose angle of radiation is modified in a manner other than by shading a beam path with a screen or mask, includes an interior light source and a first lens that is a front lens of the spotlight, with the first lens being an aspherical lens.
Use of an aspherical lens as a first lens, i.e. as a front lens of such a spotlight, ensures a more even light distribution outside of the spot setting in comparison to such spotlights known in the prior art.
The term xe2x80x9caspherical lensesxe2x80x9d means lenses in which at least one partial surface is not spherical in structure, with plane faces being always counted as spherical surfaces. Examples of aspherical lenses are lenses having one ellipsoid and one spherical surface, and lenses having one spherical surface and one hyperbolic surface. Fresnel lenses having aspherically structured partial surfaces are also aspherical lenses according to the above definition.
Advantageous and preferred embodiments of spotlights having enhanced features of this invention are described herein.
In one embodiment of a spotlight of this inventionxe2x80x94in which a second lens is placed in a light-beam path between the light source and the first lens, with a reflector, the light source, and the second lens being mounted as an optical unit that is movable along an optical axis of the spotlight relative to the first lensxe2x80x94prior-art edge-intensity increases in light distributions are entirely smoothed out, and particularly uniform lighting of the lighted area is achieved, with a high degree of variability of the angle of radiation, independently of selected settings of the angle of radiation.
In a spotlight according to the invention in which the second lens is grained on at least one surface, the graining does not need to be made as deep as graining of a second lens commonly known in the prior art. In this way, loss of light is reduced and, as is particularly important in the spot setting, greater light intensity is achieved with the same input power.
In a particularly preferred embodiment in which the second lens is an aspherical lens, light efficiency in the spot setting is increased in comparison with a second lens structured as a spherical lens, with the same input power.
Particularly uniform light distribution is achieved with embodiments of the spotlight wherein the lenses have surfaces formed in accordance with the equations disclosed and claimed herein.
In an embodiment of the spotlight according to the invention in which a spacing between the light source and the second lens is adjustable within an optical unit, it is ensured that the spotlight also has all the advantages of the spotlight disclosed in U.S. Pat. No. 4,823,243.
In an embodiment of the spotlight of the invention in which a spacing between the light source and the reflector is adjustable within the optical unit, it is ensured that the spotlight also has all the advantages of the spotlight disclosed in European Patent 0 846 913, specifically the very great variability of the angle of radiation and of the light intensity.